Transporting fluids and mixtures of fluids may require careful handling, for example, when a fluid mixture includes a toxic fluid. An example of such a fluid is sour gas, which is natural gas that may contain up to, or over, 20% hydrogen sulfide contaminant by weight. Sour gas may also contain aromatic hydrocarbons, for example, benzene, toluene, xylenes and ethylbenzene. As is well known, hydrogen sulfide and such aromatic hydrocarbons may be toxic.
For example, the presence of hydrogen sulfide (H2S) in transportable fluids can give rise to critical safety problems. In humans, the recommended exposure limit for H2S is 10 ppm per 10 minutes of exposure. The gas is immediately lethal at a concentration of about 300 ppm, which is comparable to the toxicity of hydrogen cyanide. The human nose can detect concentrations as low as 0.02 ppm and its maximum sensitivity is about 5 ppm; the nose becomes increasingly unable to detect hydrogen sulfide at concentrations of 150-200 ppm.
The presence of hydrogen sulfide and other toxic fluids also brings special demands on the materials for installations handling and the transport of fluids, as many metals are sensitive to, for example, sulfide stress cracking. During transport along a pipe, for example, fluids such as sour gas may partially separate and/or permeate the pipe, thus releasing toxic fluids into the pipe surroundings. When such a pipe includes for example an outer jacket, such escaped fluids may potentially cause burst or fracture of the pipe and/or the outer jacket.
Spoolable tubing, or tubing capable of being spooled upon a reel, is commonly used in numerous oil well operations, although other applications exist. For example, spoolable pipe may be used in gathering applications that, for example, transport produced fluids from the individual well head to transportation pipeline, or in other oil well operations include running down hole with well tools, or working over wells by delivering various chemicals down hole, and performing operations on the interior surface of the well bore. The tubes are spoolable so that a tube for example, can be used in long continuous lengths with a minimum number of joints, or with one well, and then transported on a reel to another well at a different location.
There is a need for a system that includes spoolable pipe which may not be susceptible to, for example, gas contaminants, and/or that provides for removal of such contaminants in a safe manner.
The procedure to construct a composite tube that is capable of spooling for transport or deployment, and able to resist high internal pressure loads or axial tensile or compressive loads involves using complex composite mechanics engineering principles to ensure that the tube has sufficient strength. Examples of composite tubes are presented in U.S. Pat. Nos. 5,921,285, 6,016,845, 6,004,639, 6,148,866, 6,286,558, 6,357,485, and 6,604,550 the entireties of which are incorporated herein by reference in their entireties.